点火系统外文文献翻译中英文翻译外文翻译.docx

点火系统外文文献翻译中英文翻译外文翻译.docx

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点火系统外文文献翻译中英文翻译外文翻译

IgnitionSystem

Thepurposeoftheignitionsystemistocreateasparkthatwillignitethefuel-airmixtureinthecylinderofanengine.Itmustdothisatexactlytherightinstantanddoitattherateofuptoseveralthousandtimesperminuteforeachcylinderintheengine.Ifthetimingofthatsparkisoffbyasmallfractionofasecond,theenginewillrunpoorlyornotrunatall.

Theignitionsystemsendsanextremelyhighvoltagetothesparkplugineachcylinderwhenthepistonisatthetopofitscompressionstroke.Thetipofeachsparkplugcontainsagapthatthevoltagemustjumpacrossinordertoreachground.Thatiswherethesparkoccurs.

Thevoltagethatisavailabletothesparkplugissomewherebetween20,000voltsand50,000voltsorbetter.Thejoboftheignitionsystemistoproducethathighvoltagefroma12voltsourceandgetittoeachcylinderinaspecificorder,atexactlytherighttime.

Theignitionsystemhastwotaskstoperform.First,itmustcreateavoltagehighenough（20,000+）toacrossthegapofasparkplug,thuscreatingasparkstrongenoughtoignitetheair/fuelmixtureforcombustion.Second,itmustcontrolthetimingofthatthesparksoitoccursattheexactrighttimeandsendittothecorrectcylinder.

Theignitionsystemisdividedintotwosections,theprimarycircuitandthesecondarycircuit.Thelowvoltageprimarycircuitoperatesatbatteryvoltage（12to14.5volts）andisresponsibleforgeneratingthesignaltofirethesparkplugattheexactrighttimeandsendingthatsignaltotheignitioncoil.Theignitioncoilisthecomponentthatconvertsthe12voltsignalintothehigh20,000+voltcharge.Oncethevoltageissteppedup,itgoestothesecondarycircuitwhichthendirectsthechargetothecorrectsparkplugattherighttime.

TheBasics

Beforewebeginthisdiscussion,let’stalkabitaboutelectricityingeneral.Iknowthatthisisbasicstuff,buttherewasatimethatyoudidn’tknowaboutthisandtherearepeoplewhoneedtoknowthebasicssothattheycouldmakesenseofwhatfollows.

AllautomobilesworkonDC（DirectCurrent）.Thismeansthatcurrentmoveinonedirection,formthepositivebatteryterminaltothenegativebatteryterminal.Inthecaseoftheautomobile,thenegativebatteryterminalisconnectedbyaheavycabledirectlytothebodyandtheengineblockofthevehicle.Thebodyandanymetalcomponentincontactwithitiscalledtheground.Thismeansthatacircuitthatneedstosendcurrentbacktothenegativesideofthebatterycanbeconnectedtoanypartofthevehicle’smetalbodyorthemetalengineblock.

Agoodexampletoseehowthisworksistheheadlightcircuit.Theheadlightcircuitconsistsofawirethatgoesfromthepositivebatteryterminaltotheheadlightswitch.Anotherwiregoesfromtheheadlightswitchtooneoftwoterminalsontheheadlightbulb.Finally,athirdwiregoesfromasecondterminalonthebulbtothemetalbodyofcar.Whenyouswitchtheheadlighton,youareconnectingthewirefromthebatterywiththewiretotheheadlampsallowingbatterycurrenttogodirectlytotheheadlampbulbs.Electricitypassesthroughthefilamentsinsidethebulb,thenouttheotherwiretothemetalbody.Fromthere,thecurrentgoesbacktothenegativeterminalofthebatterycompletingthecircuit.Oncethecurrentisflowingthroughthiscircuit,thefilamentinsidetheheadlampgetshotandglowsbrightly.Lettherebelight.

Now,backtotheignitionsystem,thebasicprincipleoftheelectricalsparkignitionsystemhasnotchangedforover75years.Whathaschangedisthemethodbywhichthesparkiscreatedandhowitisdistribute.

Currently,therearethreedistincttypesofignitionsystem.Themechanicalignitionsystemwasusedpriorto1975.Itwasmechanicalandelectricalandusednoelectronics.Byunderstandingtheseearlysystem,itwillbeeasiertounderstandthenewelectronicandcomputercontrolledignitionsystem,sodon’tskipoverit.Theelectronicignitionsystemstartedfindingitswaytoproductionvehiclesduringtheearly70sandbecamepopularwhenbettercontrolandimprovedreliabilitybecameimportantwiththeadventofemissioncontrols.Finally,thedistributorlessignitionsystembecameavailableinthemid80s.Thissystemwasalwayscomputercontrolledandcontainednomovingparts,soreliabilitywasgreatlyimproved.Mostofthesesystemsrequirednomaintenanceexceptreplacingthesparkplugsatintervalsfrom60,000toover100,000miles.

Let’stakeadetailedlookateachsystemandseehowtheywork.

TheMechanicalIgnitionSystem

Thedistributoristhenervecenterofthemechanicalignitionsystemandhastwotaskstoperform.First,itisresponsiblefortriggeringcoiltogenerateasparkatthepreciseinstantthatitisrequired（whichvariesdependinghowfasttheengineisturningandhowmuchloaditisunder）.Second,thedistributorisresponsiblefordirectingthatsparktothepropercylinder（whichiswhyitiscalledadistributor）.

Thecircuitthatpowerstheignitionsystemissimpleandstraightforward.WhenyouinsertthekeyintheignitionswitchandturnthekeytotheRunposition,youaresendingcurrentfromthebatterythroughawiredirectlytothepositive（+）sideoftheignitioncoil.Insidethecoilisaseriesofcopperwindingsthatlooparoundthecoiloverahundredtimesbeforeexitingoutthenegative（-）sideofthecoil.Fromthere,awiretakesthiscurrentovertothedistributorandisconnectedtoaspecialon/offswitch,calledthepoints.Whenthepointsareclosed,thiscurrentgoesdirectlytoground.Whencurrentflowsfromtheignitionswitch,throughthewindingsinthecoil,thentoground,itbuildsastrongmagneticfieldinsidethecoil.

Thepointsaremadeupofafixedcontactpointthatisfastenedtoaplateinsidethedistributor,andamovablecontactpointmountedontheendofaspringloadedarm.Themovablepointridesona4,6,or8lobecam（dependingonthenumberofcylinderintheengine）thatismountedonarotatingshaftinsidethedistributor.Thisdistributorcamrotatesintimewiththeengine,makingonecompleterevolutionforeverytworevolutionsoftheengine.Asitrotates,thecampushesthepointsopenandclosed.Everytimethepointsopen,theflowofcurrentisinterruptedthroughthecoil,therebycollapsingthemagneticfieldandreleasingahighvoltagesurgethroughthesecondarycoilwindings.Thisvoltagesurgegoesoutthetopofthecoilandthroughthehigh-tensioncoilwire.

Now,wehavethevoltagenecessarytofirethesparkplug,butwestillhavetogetittothecorrectcylinder.Thecoilwiregoesfromthecoildirectlytothedistributorcap.Underthecapisarotorthatismountedontopoftherotatingshaft.Therotorhasametalstriponthetopthatisinconstantcontactwiththecenterterminalofthedistributorcap.Itreceivesthehighvoltagesurgefromthecoilwireandsendsittotheotherendoftherotorwhichrotatespasteachsparkplugterminalinsidethecap.Astherotorturnsontheshaft,itsendsthevoltagetothecorrectsparkplugwire,whichinturnsendsittothesparkplug.Thevoltageentersthesparkplugattheterminalatthetopandtravelsdownthecoreuntilitreachesthetip.Itthenjumpsacrossthetipofthesparkplug,creatingasparksuitabletoignitethefuel-airmixtureinsidethatcylinder.

ThedescriptionIjustprovidedisthesimplifiedversion,butshouldbehelpfultovisualizetheprocess,butweleftoutafewthingsthatmakeupthistypeofignitionsystem.Forinstance,wedidn’ttalkaboutthecondenserthatisconnectedtothepoint,nordidwetalkaboutthesystemtoadvancethetiming.Let’stakealookateachsectionandexploreitinmoredetail.

TheIgnitionSwitch

Therearetwoseparatecircuitsthatgofromtheignitionswitchtothecoil.Onecircuitrunsthrougharesistorinordertostepdownthevoltageabout15%inordertoprotectthepointsfromprematurewear.Theothercircuitsendsfullbatteryvoltagetothecoil.Theonlytimethiscircuitisusedisduringcranking.Sincethestarterdrawsaconsiderableamountofcurrenttocranktheengine,additionalvoltageisneededtopowerthecoil.Sowhenthekeyisturnedtothespring-loadedstartposition,fullbatteryvoltageisused.Assoonastheengineisrunning,thedriverreleasesthekeytotherunpositionwhichdirectscurrentthroughtheprimaryresistortothecoil.

Onsomevehicles,theprimaryresistorismountedonthefirewallandiseasytoreplaceifitfails.Onothervehicles,mostnotablyvehiclesmanufacturedbyGM,theprimaryresisterisaspecialresisterwireandisbundledinthewiringharnesswithotherwires,makingitmoredifficulttoreplace,butalsomoredurable.

IgnitionCoil

Theignitioncoilisnothingmorethatanelectricaltransformer.Itcontainsbothprimaryandsecondarywindingcircuit.Thecoilprimarywindingcontains100to150turnsofheavycopperwire.Thiswiremustbeinsulatedsothatthevoltagedoesnotjumpfromlooptoloop,shortingitout.Ifthishappened,itcouldnotcreatetheprimarymagneticfieldthatisrequired.Theprimarycircuitwiregoesintothecoilthroughthepositiveterminal,loopsaroundtheprimarywindings,thenexitsthroughthenegativeterminal.

Thecoilsecondarywindingcircuitcontains15,000to30,000turnsoffinecopperwire,whichalsomustbeinsulatedfromeachother.Thesecondarywindingssitinsidetheloopsoftheprimarywindings.Tofurtherincreasethecoilsmagneticfieldthewindingsarewrappedaroundasoftironcore.Towithstandtheheatofthecurrentflow,thecoilisfilledwithoilwhichhelpskeepitcool.

Theignitioncoili